A photographer was seen with his face bleeding on the ground and at least one demonstrator was detained moments after the pope left the palace where he had spoken alongside President Dilma Rousseff, AFP correspondents said.
An officer told AFP that the police charged the crowd after someone threw a Molotov cocktail.
The demonstrators were protesting the USD 53 million in public funds spent for the pope's visit, weeks after massive protests were held across the country to denounce corruption and government waste.